This jellyfish has 2 life phases, a “polyp” form and a “medusa,” each giving “birth” to the other.
The polyp is tiny and sessile (attached to a surface; not free-floating), like a very simple sea anemone or hydroid with only a few branches. The polyps form “buds” on their sides that separate to become new individuals. In this way, the polyps can form in colonies.
The more commonly seen phase of this animal is the free-swimming “medusa,” which has the typical jellyfish form: an umbrella-like body with a stomach (manubrium) extending downward from the center. At the bottom of the manubrium is the mouth opening, with 4 frilly lobes. A fringe of up to 400 tentacles lines the edge of the “umbrella.”
This creature is transparent or translucent, sometimes faintly tinted tan, gray, white, green or blue. Four white, opaque patches sometimes appear in the body—these are the gonads (organs that produce sperm and eggs). The medusa phase is most abundant in late summer.